Russian President Vladimir Putin has been dishonest about Ukraine, President Obama said during a joint appearance with German Chancellor Angela Merkel today amid escalating tensions between government forces and pro-Russian separatists in eastern Ukraine earlier in the day.

“A few weeks ago Mr. Putin was still denying that the Russian military was even involved in Crimea. Then a few weeks later he acknowledged, 'Yeah, I guess that was our guys,'” Obama said. “And so there just has not been the kind of honesty and credibility about the situation there and a willingness to engage seriously in resolving these diplomatic issues.”

“If, in fact, Mr. Putin’s role is to allow Ukrainians to make their own decisions, then he is free to offer up his opinions about what he would like the relationship to be between Ukraine and Russia,” Obama said, adding that Ukrainians cannot accept a status as an “appendage” of Russia.

Obama called the capture and subsequent treatment of Organization of Security and Cooperation in Europe monitors by pro-Russian forces in eastern Ukraine “disgraceful and inexcusable.”

Obama and Merkel presented a united front on broader sanctions against sectors of Russia’s economy, coordinated by the U.S. and European Union, if Russia invades Ukraine or deepens its involvement in Ukraine.

“Combined with the offer that we want diplomatic solutions, it is a very necessary second component [to show] that we’re serious,” Merkel said. “There is a broad range of possibilities. We will move to the third stage” if Russia seeks to escalate tensions in Ukraine.

Obama acknowledged that the EU must have its own internal discussions about sanctions, as some of its 28 countries are more “vulnerable” to Russia -- and to prohibitions on doing business with certain Russians and Russian businesses -- than others.

Obama again called on Russia to call off armed separatists fighting with Ukrainian government forces.

“As Ukrainian forces move to restore order in Eastern Ukraine, it is obvious to the world that these Russian-backed groups are not peaceful protesters,” Obama said. “They are heavily armed militants that are receiving support from Russia.”

Obama threatened new sanctions if Russia works to destabilize Ukraine’s coming elections and touted the effect of two rounds of U.S. and European Union sanctions on prominent Russians and businesses.

They are “making an already weak Russian economy even weaker,” Obama said, speaking in the White House Rose Garden.

Merkel traveled to Washington to meet with Obama as violence escalated in eastern Ukraine.

Pro-Russian forces reportedly shot down two Ukrainian helicopters today, and Ukraine’s government in Kiev launched a major offensive against separatist forces. Ukraine’s president claimed today that “many” pro-Russian insurgents were killed or wounded in Sloviansk, the scene of the fighting, The Associated Press reported.

Russia requested an emergency meeting of the United Nations Security Council this morning, and the U.N. said the meeting would happen midday, as Obama and Merkel were to address U.S. and German reporters in the Rose Garden.

Ukraine figured to top the agenda during Merkel’s visit.

With communications halted between Obama and Russian President Vladimir Putin, Merkel has been in touch with the Russian leader. Merkel and Putin last spoke by phone Thursday morning, the AP reported. In that conversation, Merkel asked Putin to help free Organization for Security and Cooperation in Europe observers held captive by pro-Russian forces in eastern Ukraine.

The largest economy in Europe, Germany figures as a key player in Obama’s attempts to rally major sanctions on Russia’s economy, by both the U.S. and Europe, if Russia invades Ukraine.